Begin with a 12-inch ruler and show students how to hold it correctly. For demonstration purposes, you may want to use a yardstick so students can see easier or if this may cause confusion, gather students around you so they can see the 12-inch ruler.
Tell students that the inches are already numbered such 1, 2, 3 and so on. Explain to them that the long line between each number represents half. Point to the 1 and then slide your finger to the long line between the 1 and the 2. Tell them is represents 1-1/2. Repeat again for 2-1/2 and 3-1/2 until they get the idea.
State that when measuring an object, the item has to be all the way at the end of the ruler that has the 1, not at the 1, in the middle, or at the end toward the 1. Advise them if it isn't, the measurement will be incorrect.
Show them examples of how to line up a ruler next to objects correctly and incorrectly so they can see the difference. Use things such as ribbon, a book or hall pass.
Give them something to practice measuring. Now that students know that they are learning to measure using inches, allow them to practice with objects such as pencils, erasers, crayons and other things in the room. Circulate around the room to ensure they are measuring from the tip of the object and not putting the object in the middle of the ruler to get a measurement. Use items that will give students whole inch answers before asking them to measure items to the half inch. For more practice, there are Internet sites that offer games for students to practice measuring items.